Crude natural rubber is generally quite high in viscosity and therefore does not mix easily and quickly with the many additives used during processing. To facilitate these additions, such rubber usually is softened by undergoing a preliminary step called mastication.
The rubber is placed into a usual mixer, such as the Banbury, and is subjected to heat and a plasticizer (peptizer), while being mixed, for several minutes. It is then dumped, sheeted on a roll mill and cooled. The softened rubber then undergoes the mixing step.
The use of the novel processing aids of this invention eliminate the need for the mastication step. These compositions can be added directly to the crude rubber in the mixing cycle along with the other additives. It is, therefore, an object of this invention to provide novel rubber processing compositions which will facilitate the breaking of the polymer and thereby eliminate the need for both the mastication step and the peptizers used therein.
The novel processing compositions of this invention have other beneficial effects in rubber compounding. They reduce the mixing time required for the rubber compounding and provide for better dispersal of additives than traditional methods. In addition, they lower mixing temperatures and provide for improved flow, improved physical properties, improved mixing and extruding characteristics, and improved physical characteristics of the rubber. Hence, even the compounding of synthetic rubber requiring no premastication will be enhanced by the use of these formulations.
It is, therefore, a further object of this invention to provide novel rubber processing compositions which facilitate the mixing of rubber compounds with natural and synthetic rubbers in relation to time requirements, arrangement of schedule for the addition of various compounding ingredients, and the possibility of uninterrupted working with the mixed compound because of lower, safer dump temperatures without adversely affecting physical properties of said rubber compounds.